1. Field of the Invention
The present invention relates to an environmental-radioactivity measurement. More particularly, it relates to an environmental-radioactivity measurement/management system using the same measurement, and an analysis method for the radioactivity intensity.
2. Description of the Related Art
In the recommendation (: ICRP Publication 60, 1990) presented by ICRP (International Commission on Radiological Protection), ICRP has made the following recommendation: Even in the case of radiation exposure due to a natural radiation source, for example, “operations at a place at which a regulation authority concerned has declared that careful attention is required for radon, and which the authority has recognized as being an operation worksite of which this requirement holds true” should be added into the range of occupational radiation exposure. Accordingly, there is a possibility that, for example, operations at hot spring, many underground mines, and certain type of underground worksites may be operations of which this requirement holds true.
By the way, in the air at an operation worksite like this, radioactive elements of radon, i.e., a radioactive noble gas, or the series of radon's progeny nuclides (: uranium series), and radioactive elements of thoron, i.e., a radioactive noble gas as well, or the series of thoron's progeny nuclides (: thorium series) exist in a mixed state in many cases. Also, in the series of thoron's progeny nuclides, the half-life of 212Pb (Pb-212) is equal to 10.64 hours, which is comparatively long. In the series of radon's progeny nuclides, on the other hand, the half-life of 214Pb (Pb-214) is equal to 26.8 minutes, which is short. As a result, even if 214Pb is collected using a collector, 214Pb will decay before it is sent to an analysis center to undergo the measurement and analysis. Consequently, there has existed a problem that it becomes impossible to detect the radioactive elements of the series of radon's progeny nuclides.
Also, in JP-A-2002-196078, the following method has been disclosed: When plural types of radioactive elements which radiate α-rays are in a mixed state, and further, if the energies of their respective α-rays are of mutually close values, the radioactive nuclides are identified and quantified as follows: Namely, this identification and quantification is implemented not by performing a chemical separation of the radioactive elements, but by making the analysis through determination of time intervals of the pulses which have been incident into an α-ray detector.
The method disclosed in JP-A-2002-196078, however, is difficult to employ in a large number of worksites where measurement specimens are to be generally sampled. This difficulty arises from a significant cost needed at this time. Accordingly, it is requested from the viewpoint of internal exposure management that the radioactivity should be measured by using an easier and simpler method. Here, the radioactivity is caused by radon, thoron or the radioactive elements of their progeny nuclides in the air of an environment requested by a client.